Data migration technology of migrating data from a first storage system to a second storage system is known. For example, if a storage system is newly installed, data is sometimes migrated from the existing storage system to the newly installed first storage system. In addition, while the storage system is in use, there are cases where data is migrated from a high load storage system to a low load storage system. Data migration is also performed between storage apparatuses in the storage system in addition being performed between storage systems.
Patent Literature 1 discloses technology of migrating data transparently to a host computer (hereinafter referred to as the “host”) between storage systems while maintaining access from the host. According to Patent Literature 1, a first storage system (storage system as the data migration destination) is coupled between the host and a second storage system (existing storage system as the data migration source). Migration target data is migrated from the second storage system to the first storage system while the first storage system receives an access request (read request and/or write request) to the migration target data from the host. If the first storage system receives an access request to the migration target data which has not yet been migrated, it issues a read request to the second storage system in order to read data of the portion that is required for processing the received access request. The first storage system processes the foregoing received access request by using data that was acquired in response to the read request.
Moreover, for example, storage virtualization technology is also known. According to storage virtualization technology, the second storage system is coupled to the first storage system, and a storage area of the second storage system is provided to the host as a storage area of the first storage system. If the first storage system receives an access request from the host, whether the access destination according to the access request is the storage area of the first storage system or the storage area of the second storage system is specified, and, if the specified access destination is the storage area of the second storage system, the access request is transferred to the second storage system.
In addition, for example, thin provisioning is also known. Accordingly to thin provisioning, a virtual logical volume (hereinafter referred to as the “TP volume”) configured from a plurality of virtual pages (virtual storage areas) and a pool configured from a plurality of physical pages (physical storage areas) are defined. An unassigned physical page is assigned to the virtual page in response to writing into the unassigned virtual page.
Patent Literature 2 discloses technology of using a storage area of the second storage system comprising a thin provisioning function in the first storage system based on storage virtualization technology.